The present invention relates to apparatus for controlling an operational characteristic of a controlled device, e.g., the grain of a variable gain amplifier, in accordance with the position of a movable member, e.g., a manually adjustable control level. There is disclosed herein apparatus for using radiant energy to detect the position of the movable member, for applying the resulting position indicating signal to a device which generates another signal having a value indicative of the value assigned to that particular position of the movable member, and for then applying this representative signal to the controlled device for controlling its characteristic.
In the past, it has been common to control the operational characteristics of a controlled device in accordance with the position of a movable member by connecting the movable member to either a linear or rotary potentiometer, whereby movement of the movable member changed the setting of the potentiometer. The signal derived from the wiper arm of the potentiometer was then be applied to the controlled device for controlling the operational characteristic of interest. One example of such an application is the fader control commonly employed in audio consoles. In the past, these fader controls have consisted of a linear potentiometer whose settling was controlled by the operator. The voltage signal derived at the wiper arm of the potentiometer was applied to a voltage controlled amplifier (VCA) for controlling its gain.
Potentiometers, however, tend to wear with time, eventually becoming so electrically "noisy", that replacement is required. Further, there is a period of gradual deterioration between the time of first use and the time that replacement is mandated. It would be desirable to provide some manner of controlling the operational characteristic of the controlled device which avoided this operational degradation with time, preferably maintaining quiet operation indefinitely.
Conventionally, the signal used to control the operational characteristic of the controlled device was directly derived from the wiper arm of the potentiometer. The fashion in which the control voltage varied with the position of the movable member could be altered by changing the taper of the potentiometer, the response characteristics of the controlled device, or the manner of interconnection between the manually movable lever and the potentiometer. It would be desirable to provide some method of controlling a device in accordance with the position of the movable member, wherein the relationship between the position of the movable member and the controlled characteristic could be varied in a more simple and convenient manner.